1. Field
The present invention relates to an LED dimmer, an LED lighting device including the same and a method for controlling dimming of the LED light emitting device, and more particularly to an LED dimmer capable of controlling luminance of an LED light emitting device according to switching operation of a power switch, an LED lighting device including the same, and a method for controlling dimming of the LED light emitting device.
2. Discussion of the Background
Dimming operation of a light emitting diode (LED) refers to operation of changing luminance or brightness of an LED lighting device according to external disturbance applied thereto, and an LED dimmer refers to a device that performs a dimming control function within such an LED lighting device. Such an LED dimmer is provided to an LED lighting device in order to reduce power consumption of the LED in the LED lighting device while securing efficient operation thereof.
Particularly, heat generated from the LED due to continuous light emission of the LED causes deterioration in efficiency of lighting operation. In addition, although use of DC voltage for the LED lighting device does not require separate rectification operation and allows the LED lighting device to directly employ line power, there is a limit in application.
On the other hand, use of alternating current power requires separate rectification operation for efficiency improvement in power use and allows the LED lighting device to perform light emitting operation using a rectified DC voltage. Particularly, an LED lighting device employing an LED has a problem in terms of efficient use of applied AC power. Particularly, luminance or power supply of the LED lighting device must be controlled according to user input, operation conditions, or states of the LED lighting device.
In order to control luminance of such a lighting device, various types of dimmers are used. In addition, to receive user input for controlling luminance of the lighting device, various dimmer switches are used. As such a dimmer switch, a dial-type dimmer switch capable of controlling not only on/off of the lighting device but also a dimming level thereof is broadly used in the art. When such a dial-type dimmer switch is used, the dimming level of the lighting device is determined by a user adjusting the dial-type dimmer switch, and luminance control of the lighting device can be easily performed according to the determined dimming level. However, a lighting device configured to control only on/off of the lighting device using a non-dial-type switch (for example, a button type switch, a latch type switch, and the like) requires dimming control, but has a problem of difficulty in dimming control. Accordingly, various techniques for performing dimming control of the lighting device using the non-dial-type switch, that is, techniques relating to the switch dimmer, have been actively developed. One example of conventional techniques relating to the switch dimmer is disclosed in U.S. Pat. No. 4,649,323 (Patent Document) entitled “MICROCOMPUTER-CONTROLLED LIGHIT SWITCH”, in which luminance of the lighting device is controlled using a pair of non-latch type switches. More specifically, the invention (Conventional Technique 1) disclosed in Patent Document 1 is configured to increase or decrease luminance of the lighting device by determining the case where one of switches is pushed for a long period of time as a “preset” mode based on a pushed state of the switches, and to store luminance of the lighting device at a point of time when no switch is pushed by a user. In addition, Conventional Technique 1 is configured such that, when one of the switches is pushed for a short period of time (that is, when the switch is tapped), current luminance of the lighting device can be changed to a preset level, a full-on level, and an off level depending upon the pushed switch (a luminance increase switch or a luminance decrease switch). However, such Conventional Technique 1 has problems in that i) a user must perform a separate preset setting process; ii) two switches dedicated for dimming are required; iii) this technique can be applied only to a button type switch and cannot be applied to a latch type switch; iv) it is necessary to measure a period of time for which the switch is pushed by a user; v) this technique does not allow accurate control of luminance, and the like. On the other hand, in order to solve the aforementioned problems, U.S. Pat. No. 7,235,933 (Patent Document 2) entitled “REVERSIBLE DIMMER DEVICE OF GAS DISCHARGE LAMPS AND THE CONTROL METHOD FOR LIGHT ADJUSTING THEREOF” discloses a technique capable of controlling luminance of a lighting device using a single power switch that can turn on/off power input to the lighting device. The invention (Conventional Technique 2) disclosed in Patent Document 2 is configured to detect a state of the power switch in response to user manipulation and to control luminance of the lighting device according to state variation of the power switch. More specifically, Conventional Technique 2 controls luminance of the lighting device based on the number of On/Off times and timing by recognizing the case where the power switch is rapidly turned off/on in a short period of time in response to user manipulation as a user command for luminance control. However, Conventional Technique 2 is a lighting device based on sensing of power switch off-time and has a problem in that this technique requires a power storage device for power supply to a logic control circuit during off-time. That is, since Conventional Technique 2 necessarily includes the power storage device such as a capacitor, there are problems in that the lighting device has a complicated circuit configuration, is difficult to achieve size reduction, and has short lifespan due to short lifespan of the capacitor. On the other hand, as another example of the lighting device based on off-time sensing, US Patent Publication No. 2010/0148691 (Patent Document 3) entitled “DRIVING CIRCUIT WITH DIMMING CONTROLLER FOR DRIVING LIGHT SOURCES” discloses a dimming control technique that is very similar to Conventional Technique 2. FIG. 1 is a block diagram of an LED lighting device according to an invention (Conventional Technique 2) disclosed in Patent Document 3. As shown in FIG. 1, the lighting device according to Conventional Technique 3 includes a power switch 04, an AC/DC converter 06, dimming controller 08, a power converter 10, an LED string 12, and a current sensor 14. The power switch 04 serves to selectively apply AC voltage to the LED lighting device in response to user manipulation, and the AC/DC converter 06 outputs DC voltage by converting the input AC voltage into the DC voltage through full-wave rectification by a bridge diode, and the power converter 10 receives and stabilizes the DC voltage to supply stabilized power to the LED string 12. With regard to dimming control function of the LED lighting device according to Conventional Technique 3, dimming controller 08 is configured to monitor an operation state of the power switch 04 by monitoring whether DC voltage is input from the AC/DC converter 06, and to change the dimming level each time of detecting turn-off operation of the power switch 04. That is, in Conventional Technique 3, dimming controller 08 is configured to change a counter value each time of detecting that the power switch 04 is turned off, and to perform dimming control of the LED lighting device according to a changed counter value when the power switch is turned on again. To perform this function, dimming controller 08 of Conventional Technique 3 must be maintained in a driven state while the power switch 04 is turned off, that is, during off-time, and thus the LED lighting device of Conventional Technique 3 includes a capacitor C10 configured to supply power to dimming controller 08 during off-time. However, Conventional Technique 3 has problems in that i) since it is necessary to detect the operation state of the power switch 04, the lighting device has a complicated circuit configuration; and in that ii) since the lighting device necessarily includes an energy charge/discharge device, such as a capacitor and the like, for supplying operation power to dimming controller 08 during off-time, the LED lighting device has a complicated circuit configuration, is difficult to reduce in size, has short lifespan due to short lifespan of the capacitor, and requires high manufacturing costs. Moreover, Conventional Technique 3 has problems in that (iii) since input power passes through the capacitor that is a power source in an off-state, discordance between input current and input voltage causes decrease of power factor (PF) and increase of total harmonic distortion (THD); and (iv) since dimming controller 08 must perform sensing operation prior to other operations when the power switch 04 is turned on and supply power again, time delay occurs in operation stabilization of the LED lighting device, causing very unstable operation due to rapid variation of power.